Urban Forests Battle Global Warming
A survey of North American cities by the American Council for an Energy-Efficient Economy and the Global Cool Cities Alliance found that confronting the challenges of extreme weather, adapting to a changing climate, and improving the health and resiliency of urban populations are driving cities to develop and implement strategies to reduce excess urban heat.
Nearly two thirds of the cities surveyed cited local extreme weather events as a key reason for initiating urban heat island mitigation strategies.
“U.S. cities are waking up to the growing threat of urban heat and employing a number of innovative approaches suited to their location and priorities,” said ACEEE researcher and report author Virginia Hewitt. “Our report will help local planners adapt these practices to even more communities across the country.”
ACEEE and GCCA surveyed 26 cities in the U.S. and Canada representing all of the major climate zones, geographies, and city sizes. Despite the diversity of the respondents, several common themes emerged. Local governments are “leading by example” by requiring use of “cool” technologies, such as reflective roofs on municipal buildings, lining city streets with shade trees, and raising public awareness. Additionally, more than half of the cities have some kind of requirement in place for reflective and vegetated roofing for private sector buildings. Almost every city had policies to increase tree canopy and manage stormwater.
By addressing their urban heat islands, cities are more effectively delivering core public health and safety services, making them attractive places to live, work, and play.
The report includes case studies on how several cities have responded to urban heat, demonstrating the variety of strategies employed. In response to a study that found that Houston’s roofs and pavements can reach 160⁰F, the city now requires most flat roofs in the city to be reflective. After an extreme heat wave in 2008, Cincinnati lost much of its urban canopy, and instituted an aggressive forestry plan. Washington D.C. has instituted a wide suite of programs such as Green Alleys, which helps residents manage excess stormwater by replacing pavement with grass and trees, and requiring reflective roofs on all new buildings.
Most city governments are not acting alone to reduce excess heat.
States, neighboring jurisdictions, utilities, developers, contractors, and local building owners are collaborating to create incentives for communities to reduce urban heat and mainstream these practices.
“We recognized a number of years ago that keeping New York cooler was an important part of protecting public health and becoming more resilient. We started with cool-roof volunteer programs that raised awareness and understanding, while coating 5 million square feet of rooftops. These voluntary efforts led to the cool roof ordinance requiring investments in reflective roofs on certain buildings,” said Wendy Dessy of NYC Service.